1. Field of the Invention
This invention relates to a fuel injected system for a direct injected engine and more particularly to an improved fuel supply arrangement for an outboard motor incorporating a direct injected system.
2. Description of Related Art
As is well known, in all fields of engine design there is an increasing emphasis on obtaining more effective emission control, better fuel economy and, at the same time, continued high or higher power output. This trend has resulted in the substitution of fuel injection systems for carburetors as the engine charge former. In the common systems used, fuel is injected into an intake air manifold. In order to obtain still further improvement, direct injection systems are being considered. These systems inject fuel directly into the combustion chamber and thus have significant potential advantages.
This direct injection, however, means that the pressure into which the fuel is injected is higher than with manifold injection systems wherein the pressure is at substantially atmospheric or even below. Electric pumps are not totally capable of supplying such high pressures.
In order to supply the necessary pressure for a direct cylinder injection, it has been proposed to employ a fuel supply system of the type used with manifold injection systems with the addition of a high pressure mechanical pump to supply the pressures required for direct cylinder injection. This is comprised of an engine driven pump which supplies fuel to a vapor separator in which the electrically operated fuel pump that is driven off the engine and which can generate higher pressures as required by the direct injection system. This type of system can be quite effective.
However, in connection with outboard motors, the direct injection system causes problems in other aspects.
Because of frequent use under high load and low speed conditions, engines for the outboard motors consume a large amount of fuel relative to other engines such as automobile engines. The larger the engines, the more the required fuel per unit time. It could be one idea to employ a single high pressure fuel pump that has large capacity of fuel supply. However, redevelopment of such a fuel pump is not much advantageous because it could be costly. Procurement of it from parts suppliers might be more difficult because this kind of fuel pump requires special specifications. In either case, if possible, a new fuel pump would be too bulky for being placed in a small space around the engine surrounded by a protective cowling and in addition it would take much time for the fuel pump to obtain reliability on components and parts.
It is, therefore, a principal object of this invention to provide a fuel supply arrangement that can supply sufficient fuel required by engines at all times without difficulties in obtaining suitable fuel pumps.
Further, conventional fuel pumps are usually driven by existing engine components such as a camshaft that is indispensable for four cycle engines. However, a number of outboard motors incorporate a two cycle engine that has no camshaft. In addition, only very small space is remained for employing new components around the engine that is surrounded by a cowling.
It is, therefore, another object of this invention to drive a fuel pump with another drive measure that replaces the camshaft in simple and compact nature.
For a direct fuel injected engine with multiple cylinders, a relatively long size fuel supply rail is attached to the plurality of fuel injectors. Because of the nature of its mechanical drive, the fuel pump is usually placed at the one end of the fuel supply rail. Due to this arrangement, the longer the distance from the fuel pump, the larger the fuel pulsation. The fuel injectors placed more remotely from the fuel pump in the fuel supply rail are most effected. Meanwhile, injection amounts are controlled based upon a fixed fuel pressure and time of injection varied in response to the requirements from the engine. Accordingly, fluctuations in fuel pressure caused by the pulsation give rise to incorrect controls and difficulties in control of emissions.
It is, therefore, still another object of this invention to improve accuracy of the injection control in multi-cylinder engines for outboard motors, but not limited.
Another problem arises in connection with accumulated tolerances. The direct injection system needs a number of components such as a high pressure fuel pump, a fuel supply conduit and fuel injectors except for a control unit. Usually, some of these components are unified together and form a fuel injection unit. Since each component has own tolerance, the unit holds accumulated tolerances and in addition the engine, on which the unit is mounted, itself contains accumulated tolerances also. Thus, if the fuel injection unit is mounted, for example, on a cylinder body with one part and on a cylinder head with another part, it is quite difficult to place fuel injectors at accurate positions due to the accumulated tolerances. This kind of difficulty may occur with other components of the unit also.
In automobile technology, for instance, these accumulated tolerances are absorbed with flexible members such as elastic pipes. However, because of the nature of its flexibility, it is difficult to assemble them with other components and in the assembling work skilled techniques are required. In addition, due to the flexibility, such members are somewhat inferior in rigidity or stiffness and tend to invite deterioration in endurance when much stress is exerted. Thus, these members are not suitable for outboard motors that generate much vibration therein relative to automobiles.
It is, therefore, yet another object of this invention to provide a mounting arrangement for direct injection components that can resolve the problem of accumulated tolerances and keep rigidity and endurance even used for outboard motors.